(a) Field of the Invention
The present invention relates to a method and a system for charging a battery of a hybrid electric vehicle driven by power of an engine and/or a motor.
(b) Description of the Related Art
As is well known, due to increases in oil prices and exhaust gas regulations, eco-friendly policies and fuel efficiency improvement have been researched in the development of a vehicle. Accordingly, vehicle manufacturers have developed a technology for reducing fuel and decreasing exhaust gas to meet eco-friendly policies and improve fuel efficiency. Additionally, the vehicle manufacturers have focused efforts in developing a technology of a hybrid electric vehicle (HEV) which efficiently combines and uses power of an engine and power of a motor to achieve high fuel efficiency.
FIG. 1 illustrates an exemplary configuration of a conventional parallel hybrid electric vehicle.
Referring to FIG. 1, the hybrid electric vehicle may include an engine 10, a driving motor 20, an engine clutch 30 for combining or releasing power between the engine 10 and the driving motor 20, a transmission 40, a differential gear device 50, a battery 60, a starting/generating motor 70 for starting the engine 10 or generating power to be output by the engine 10, and a plurality of wheels 80.
Further, the hybrid electric vehicle may include a hybrid control unit (HCU) for controlling entire operations of the hybrid electric vehicle and a battery control unit (BCU) 120 for managing and controlling the battery 60. The battery control unit 120 may be called a battery management system (BMS).
The constituent elements of the hybrid electric vehicle are obvious to those skilled in the art, and thus a more detailed description will be omitted. The starting/generating motor 70 may be called an integrated starter and generator (ISG) or a hybrid starter and generator (HSG) in the known art.
The hybrid electric vehicle may be driven in a driving mode, such as, an electric vehicle (EV) mode using only power of the driving motor 20; a hybrid electric vehicle (HEV) mode using torque of the driving motor 20 as auxiliary power while using torque of the engine 10 as main power; and a regenerative braking (RB) mode collecting braking and inertia energy through power generation of the driving motor 20 to charge the battery 60 during braking or driving using the inertia of the vehicle.
As described above, the hybrid electric vehicle uses both mechanical energy of the engine and electric energy of the battery, uses an optimum operation region of the engine and the driving motor, and collects the energy of the driving motor while braking, thereby improving fuel efficiency and efficiently using the energy. Moreover, in the hybrid electric vehicle, a driving method may be generally divided according to a state of charge (SOC) of the battery 60.
FIG. 2 is an exemplary diagram illustrating an SOC state of the battery 60 according to a driving method of the hybrid electric vehicle. Referring to FIG. 2, the battery 60 of the hybrid electric vehicle may be divided into a critical overcharge region CH (critical high), an overcharge region H (high) a normal charge region B (normal), a low charge region L (low) and a critical low charge region CL (critical low) according to an SOC. The low charge region may be divided approximately in half to be two regions L1 and L2.
A battery control unit 120 of the hybrid electric vehicle may perform part load charge control, idle charge control, and power limit control to maintain the SOC of the battery 60 as illustrated in FIG. 2. Based on the contents illustrated in FIG. 2, the part load charge control is generally performed when the SOC of the battery is in the normal charge region N. The idle charge control is generally performed when the SOC of the battery is in the upper low charge region L1. The power limit control is generally performed when the SOC of the battery is in the lower low charge region L2 and the critical low charge region CL.
When a driver accelerates during driving and the engine is maintained in an operation state, the part load charge control controls the rotation of the driving motor 20 to generate power of the engine 10 to charge the battery with the output power. While the vehicle accelerates, the part load charge control may maintain a SOC by using a redundant power of the engine.
The idle charge control controls the rotation of the starting/generating motor 70 to generate power of the engine 10, regardless of manipulation of the accelerator pedal, the brake pedal and a vehicle speed, to change the low SOC of the battery to charge the battery with the output power. The idle charge control is control of charging the battery in order to get out of a charge insufficient state of the battery 60 regardless of a vehicle speed.
The power limit control limits power used in electronic equipment of a high voltage power module system. However, since the hybrid electric vehicle repeatedly stops when running in a congested area, a possibility of the part load charge control using the driving motor 20 decreases so the SOC of the battery lowers.
Accordingly, when the hybrid electric vehicle runs in a congested area, a hybrid control unit 110 and/or the battery control unit 120 may perform the idle charge control mode using the starting/generating motor 70 having poor charging efficiency to prevent the SOC of the battery from being decreased.
Further, since the hybrid control unit 110 and/or the battery control unit 120 of the hybrid electric vehicle according to the exemplary embodiment of the related art charge the battery 60 only with power by regenerative braking of the driving motor 20 as illustrated in FIG. 3, when an accelerator pedal position sensor (APS) and a brake position sensor (BPS) are off (e.g., when a driver does not manipulate the accelerator pedal and the brake pedal), in other words, the hybrid electric vehicle performs coasting, charging efficiency is not high.
The above information disclosed in this section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.